This invention relates to a steering mechanism that enables a vehicle to be make small sharp turns at a large steering angle, the vehicle to which the steering mechanism is applied, and a system for controlling the steering mechanism.
With reference to FIGS. 1 through 4, there are shown tie rods 41, 55, knuckle arms 42, 56, a king pin 43, a tie rod end 44, a steering shaft 51, a suspension arm 52, a pinion 53, a rack 54, a steering housing 57, a worm mechanism 58, a worm 58-1, a sector gear 58-2, a sector shaft 58-3, and a Pitman arm 59.
In order for a four-wheeled vehicle to turn smoothly, it is required that the wheels have the same turning center. To this end, conventional steering mechanisms employ a link mechanism using a knuckle arm, by way of example.
As shown in FIG. 1, a conventional steering mechanism has the tie rod 41 connected to one end of the knuckle arm 42 at the tie rod end 44, with the other end of the knuckle arm 42 being secured to the king pin 43 of the corresponding left or right wheel. If the knuckle arms 42 are angled in such a manner that extensions of the knuckle arms 42 of the left and right wheels intersect the center A of a rear axle 45, the turning centers of the wheels will be the same. The turning centers 0 are formed on an extension of the rear wheel axle, as illustrated.
In a rack-and-pinion steering mechanism, which is one of the conventional steering mechanisms, the tie rod 55 is oscillated to the left and right by the rack 54 and pinion 53 as the steering shaft 51 is rotated, as shown in FIG. 2, so that a wheel connected to the knuckle arm 56 is turned about the king pin to effect steering. A steering mechanism other than of the rack-and-pinion type employs a worm arrangement shown in FIG. 3. All of the above configurations make use of a link mechanism based on the principle shown in FIG. 1.
With these conventional vehicle steering mechanisms, a state in which the tie rod 55 and knuckle arm 56 fall on the same straight line represents the steering limit angle. This limits the ability of the vehicle to make small sharp turns. The limit angle ordinarily is about 45.degree..
Even if it were made possible for the steering angle to exceed the conventional limit angle and attain a value of, say, 90.degree., a rear-wheel drive vehicle would be incapable of traveling with the steering angle set at 90.degree. because the direction in which the driving force is applied would be at right angles to the direction of the wheels. Thus, even if a sufficiently large steering angle could be obtained with the conventional steering mechanism, wheel lock-up might occur with a rear-wheel drive vehicle and make travel impossible.